Igniting an underground coal seam in an underground coal gasification process, ucg

ABSTRACT

An ignition apparatus ( 150 ) configured to ignite an underground coal seam ( 151 ). The ignition apparatus ( 150 ) comprising an ignition system, a positioning system, a sensor ( 170 ) and a controller ( 165 ). The ignition system comprises ignition means and an ignition tool ( 155 ) for igniting the underground coal seam ( 151 ) from within the well channel ( 154 ) or well liner encasing the well channel ( 154 ). The positioning system comprises coiled tubing ( 156 ) connected to the ignition tool ( 155 ) and extendible through a well head ( 153 ) within the well channel ( 154 ) to position the ignition tool ( 155 ) at a desired location within the well channel ( 154 ). The positioning system further comprises a spool ( 157 ) for transporting and dispensing the coiled tubing ( 156 ).

FIELD OF THE INVENTION

This invention relates to a method and apparatus for igniting anunderground coal seam, for in-situ conversion of coal to product gas.

BACKGROUND OF THE INVENTION

Underground coal gasification (UCG) is a process by which product gas isproduced from a coal seam by heating the coal in situ in the presence ofan oxidant. The product gas is typically referred to as synthesis gas orsyngas and can be used as a feedstock for electricity or chemicalproduction, for example.

Conversion of coal into product gas takes place in a well whichtypically includes a well channel of sorts extending through the coalseam. Such a channel can be formed by one or more bore holes drilledinto the coal seam that are in fluid communication with one another. Thechannel is also in fluid communication with an injection well, aproduction well as well as perhaps one or more ignition or service wellsthat extend from ground level to the well channel. Typically, oxidant isinjected into the well channel via an injection well to promotecombustion. Typically, an ignition source for initiating combustion ofthe coal seam is introduced into the well channel via an ignition well.Combustion can also be initiated using an ignition device, whereby anignition device that is capable of igniting coal is inserted into thewell channel via an ignition or injection well.

A coal seam panel is typically referred to as a coal gasifier.Gasification occurs adjacent a combustion zone of the well/gasifier andthe coal is partially oxidized to produce product gas of low or mediumheating value. Hot product gas flows from the gasification zone andexits the ground from a well head of the production well. As coal isconsumed or gasified, a gasifier cavity within the coal seam developsand the channel grows in size.

One of the major challenges for UCG is to ignite the coal underground,particularly in a safe and cost effective manner. Several methods havebeen proposed and used. One such method involves dropping hot coal orlowering an electrical heat resistance device into a verticallyextending ignition well directly into an intended combustion zone andthen injecting oxygen into the combustion zone via the injection well sothat combustion is autogenous. Another method involves dropping volatilechemicals such as TEB or silane which spontaneously ignite on contactwith air to start ignition followed by the supply of ignition fuel andoxidant to the intended combustion zone so that combustion isautogenous.

One problem associated with UCG is that a combustion front produced at acombustion zone does not always progress along a coal seam as proposedin theory, and practically a coal seam may need to be reignited atdifferent sites along the coal seam so as to maximise the production andlife of the coal gasifier.

One of the problems associated with UCG when employing a well channelthat extends substantially horizontally through the coal seam is thatmore than one vertically extending ignition well (bore hole) may berequired in order to ignite/re-ignite the coal seam/gasifier at multiplelocations, as installing ignition wells is an expensive and timeconsuming process. In addition, the use of TEB or silane can bedangerous for handlers due to the highly volatile nature of the materialwhen exposed to air and any mistake in handling such materials canexpose them to air and initiate fire or explosion events.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method orapparatus for igniting (or re-igniting) coal of an underground coal seamin a safe and/or cost effective manner, or to provide the public with auseful or commercial choice.

According to a first aspect of the present invention, there is providedan ignition apparatus for igniting an underground coal seam from withina well channel that extends through the seam, said apparatus comprising:

an ignition system comprising ignition means and an ignition tool forigniting the underground coal seam from within the well channel; and

a positioning system comprising coiled tubing connected to the ignitiontool and extendible within the well channel to position the ignitiontool at a desired location within the well channel.

According to a second aspect of the present invention, there is providedan ignition system comprising ignition means and an ignition tool forigniting an underground coal seam.

According to a third aspect of the present invention, there is providedignition means for igniting an underground coal seam.

According to a fourth aspect of the present invention, there is providedan ignition tool for igniting an underground coal seam.

According to a fifth aspect of the present invention, there is provideda positioning system comprising coiled tubing extendible within a wellchannel to position an ignition tool at a desired location within thewell channel.

According to a sixth aspect of the present invention, there is provideda method of igniting an underground coal seam from within a well channelthat extends through the seam, said method comprising the steps of:

(1) moving an ignition tool of an ignition apparatus into the wellchannel; and

(2) igniting the underground coal seam at one or more locations withinthe well channel using the ignition tool,

wherein the ignition apparatus comprises:

an ignition system comprising ignition means and the ignition tool; and

a positioning system comprising coiled tubing connected to the ignitiontool and extendible within the well channel to position the ignitiontool at a said location within the well channel.

Integers of the first to sixth aspects of the invention are describedbelow, including in the detailed descriptions of the embodiments of theinvention section.

The invention is particularly suited to well channels that extendhorizontally or substantially horizontally though a coal seam/gasifieror otherwise follow a non-vertical or non-linear course. That is, theinvention is particularly suited for igniting coal seam zones that arenot immediately below or immediately adjacent a bottom of an injection,ignition or other type of service well.

The ignition means can ignite the coal seam in any suitable way. Theignition means can directly ignite the coal seam itself, or ignitecombustible fluid (eg. liquid or gas) either resident in the wellchannel or supplied to the well channel (eg. supplied as either aliquid, gas or solid).

In one embodiment, the ignition means comprises an electrical sparkgenerator (eg. spark plug) and a power supply for generating the spark.The power supply can be located above ground or the spark generator canbe powered by an in seam turbine and transformer electrically connectedto the spark generator. The ignition means can further comprise anignition fuel source and/or oxidant source for further initiating and/orfueling combustion.

In another embodiment, the ignition means comprises an electrical heatresistor (eg. glow plug) and a power supply for electrifying theresistor. The resistor can, for example, generate about 180 kW of heat.The power supply can be located above ground or the electrical heatresistor can be powered by an in seam turbine and transformerelectrically connected to the resistor. The ignition means canoptionally further comprise an ignition fuel source and/or oxidantsource for further initiating and/or fueling combustion.

In another embodiment the ignition means comprises at least one type ofignition chemical (ignition chemical source). The ignition chemical canbe a pyrophoric substance—eg. liquid such as triethylboron (TEB), gassuch as silane, solids such as phosphorus or alkali metal, or apyrophoric chemical and hydrocarbon mixture such as TEB vaporized inmethane, or a pyrophoric chemical and an inert gas such as TEB andnitrogen. The hydrocarbon or inert gas flow can help transport/vaporizethe pyrophoric chemical or slugs/plug flows of the pyrophoric chemicalto the ignition tool. The ignition means can further comprise anignition fuel source and/or oxidant source for further initiating and/orfueling combustion.

In yet another embodiment the ignition means comprises pure oxygen orsubstantially pure oxygen that ignites the coal seam directly. Theignition means can further comprise an oxidant source for fuelingcombustion.

The ignition tool can be of any suitable size, shape and constructionand can be made of any suitable type of material or materials. In itssimplest form, the ignition tool can be in the form of an end nozzle orprobe for the coiled tubing. In a more complex form, the ignition toolcan contain the ignition means and/or other components of the ignitionapparatus.

The ignition tool can comprise a tool body. The body can be of unitaryconstruction or can comprise two or more connectable body pieces. Thebody can be made of any suitable material or materials, includingstainless steel and carbon steel. If the ignition tool/body is to have asacrificial piece (eg. a blow-out plug or cap), then that piece can bemade of metal or non-metallic materials such as plastic or rubber thatcan deform or melt.

The ignition tool or the tool body can have any suitable outer diameterand length. For example, the ignition tool or the tool body can have anouter diameter of about 2 inches, 3 inches or 4 inches, for example.Preferably the ignition tool or the tool body has a diameter of about 2inches.

The body pieces can be screwed together. The body can house the ignitionmeans or not. The tool body can have an inlet end and outlet end andthese can be located at opposed ends of the body. The outlet end of thebody can be tapered or otherwise shaped so as to reduce resistance whenmoving the ignition tool to its intended location within the coal seam.The inlet end of the body can be adapted to be connected to the coiledtubing.

The ignition tool can be connected to the coiled tubing in any suitableway. The tool body can be connected to the coiled tubing in afluid-tight manner or not. The ignition tool body can be releasablyconnected or permanently connected to the coiled tubing. Preferably thebody is connected to an end of the coiled tubing by way of a screwthread or weld.

The coiled tubing can be of any suitable size, shape and constructionand can be made of any suitable material or materials. Moreparticularly, the coiled tubing can be of any suitable length anddiameter. Preferably, the coiled tubing is made of metal, such asstainless steel, carbon steel or copper. The coiled tubing can be ofunitary construction or can comprise two or more connectable tubepieces. A preferred outer diameter for the coiled tubing is two inches.

The coiled tubing can comprise a single tube (line) connected to thetool body. The coiled tubing can alternatively comprise at least oneinner tube (inner line) extending within an outer tube (outer line),wherein one or both of the inner and outer tubes are connected to thetool body. That is, the coiled tubing can comprise at least one innertube and an outer tube that extend concentrically relative to oneanother. More than one inner tube may extend within the same outer tube.A preferred diameter for the outer tube is two inches whereas apreferred diameter for the inner tube is ¾ inches.

The positioning system can further comprise a spool from which thecoiled tubing is unspooled. The spool can be of any suitable size, shapeand construction and can be made of any suitable material or materials.Preferably, the spool can unspool coiled tubing having a length of atleast about, 300 m, 400 m, 500 m, 600 m, 700 m, 800 m, 900 m, 1000 m,1100 m or 1200 m.

The ignition fuel source can feed ignition fuel to or in close proximityof the ignition tool either within a tube of the coiled tubing orexternally of the coiled tubing but within the well channel. Theignition fuel can be in the form of a solid or fluid, such as a gas orliquid. The ignition fuel can be a combustible hydrocarbon-based fluidsuch as methane, propane, butane or mixtures thereof. The ignition fuelcan be a pyrophoric gas or liquid. The ignition fuel source can be atank/cylinder of compressed combustible gas or liquefied gas. Theignition fuel source can be connected directly or indirectly to thecoiled tubing in a fluid-tight manner.

The ignition apparatus can comprise an oxidant source that can feedoxidant to or in close proximity of the ignition tool either within thecoiled tubing or externally of the coiled tubing but within the wellchannel. The oxidant can be in the form of a solid or fluid, but ispreferably a fluid such as air (approximately 20% oxygen), air or adifferent gas/gas mixture enriched with oxygen (greater than about 20%oxygen, or about 30% to 80% oxygen), or substantially pure oxygen. Theoxidant source can comprise an air compressor, a tank/cylinder ofcompressed air or oxygen, an air separation unit, or a tank/cylinder ofliquid oxygen, for example. The source of oxidant can be connecteddirectly or indirectly to the coiled tubing in a fluid-tight manner. Thesource of oxidant can be connected directly or indirectly to a well headof an injection well such that oxidant is injected into the well ratherthan the coiled tubing.

The ignition chemical source can feed ignition chemical to or in closeproximity of the ignition tool either within the coiled tubing orexternally of the coiled tubing but within the well channel. As alreadymentioned, the ignition chemical can be in the form of a solid or fluid,such as a gas or liquid. The source of ignition chemical can be apressurised or non-pressurised tank/cylinder containing such a chemical.The ignition chemical can be a pyrophoric gas or liquid. The ignitionchemical source can be connected directly or indirectly to the coiledtubing in a fluid-tight manner.

As mentioned, the coiled tubing can comprise a single tube. The tube canbe used to convey one or more electrical cables/lines (for power ordata) from above ground to the ignition tool body. The tube can be usedto feed ignition fuel and/or ignition chemical to the ignition toolbody.

As mentioned, the coiled tubing can comprise two or more tubes (lines)or more than two tubes, in which case the tubes could extendconcentrically (one within the other). An inner tube can feed ignitionfuel and/or ignition chemical to the ignition tool body. An outer tubecan feed oxidant to the ignition tool body. The outer tube can alsoconvey electrical (power or data) cables of the ignition apparatus.

For ignition apparatus comprising a single tube (‘single coil tubing’),oxidant injected into the well may flow externally of the tube. Also forignition apparatus comprising a single tube, ignition fuel and/orignition chemical injected into the well may flow within the tube. Forignition apparatus comprising concentric tubes (‘concentric coiledtubing’), oxidant injected into the well may flow within the outer tube(preferably as well as in the well itself externally of the outer tube)and ignition fuel may flow within the inner tube.

If using a single tube or concentric tubes, the (outer) tube can be madeof stainless steel or carbon steel. If air is used as the oxidant, theouter tube can be made of carbon steel and the inner tube can be made ofcopper. If air or oxygen is used as the oxidant, the outer tube can bemade of stainless steel and the inner tube can be made of copper orstainless steel.

The coiled tubing can further house other components of the ignitionapparatus including components of the ignition tool, sensors and, asmentioned, power or data cables.

The coiled tubing can comprise heat-exchange formations, such as fins orvanes extending from a tube of the coiled tubing, for cooling aninterior of the tube.

The coiled tubing can comprise positioners, such as fins or vanes, thatextend from a tube of the coiled tubing and help position the ignitiontool within the well channel (or well liner, if present). That is, theyhelp centralise the ignition tool within the well channel (or wellliner, if present).

The ignition tool can comprise at least one inlet in the body that is influid communication with at least one tube of the coiled tubing.However, it need not be a fluid-tight connection. The inlet can be ofany suitable size and shape. The inlet can be provided by a mere openingin the body or a pipe (spigot) that extends within and/or externally ofthe body. An electrical cable, sensor or other component of the ignitionassembly can extend through the inlet. Ignition fuel and/or ignitionchemical can be fed through the inlet.

The ignition tool can comprise a first inlet connected to an inner tubethat feeds ignition fuel and/or ignition chemical to the body. Theignition tool can comprise a second inlet connected to an outer tubethat feeds oxidant or conveys a cable (power or sensor) or sensor to thetool body.

The ignition tool can comprise at least one outlet from the tool bodythat is in fluid communication with the at least one inlet. That is, theignition tool can comprise a passage extending between the inlet andoutlet. However, it need not be a fluid-tight communication. The outletcan be of any suitable size and shape. The outlet can be provided by amere opening in the body or a pipe (spigot) that extends within and/orexternally of the body. An outlet of reduced diameter can help directflames away from the tool body, for example.

The tool body can comprise a detachable cap or plug (blow-out plug)covering an outlet from the body, that can be detached from a remainderof the body prior to ignition. The cap or plug can be bull nose, longnose or conical in shape. Detachment can be achieved in any suitableway. For example, an increase in gas pressure due to oxidant, ignitionfuel or ignition chemical flow through the body can be used to detachthe cap or plug. The cap/plug piece can friction fit to a remainder ofthe tool body. If in the form of a plug, a stem of the plug can frictionfit to the outlet from the body using an o-ring that extends around thestem.

In addition to the inlet/s and outlet/s, the ignition tool can have oneor more intakes extending through the body for drawing oxidant/gas fromthe well channel into the body passage by way of a Venturi effect whenignition fuel and/or oxidant flows through the passage to the outletfrom the body.

The ignition tool can comprise a mixing chamber located within the toolbody within which the ignition fuel, oxidant and/or ignition chemicalmix. Mixing can be achieved in any suitable way. Typically this willinvolve providing turbulence and/or resistance to flow of the gasesthrough the mixing chamber. To that end, the mixing chamber can compriseat least one mixing structure or device, such as a Venturi device, oneor more baffles (eg. spirals) or other turbulence-creators locatedwithin the mixing chamber (that create a pressure differential for thetwo gas streams to mix) or that define walls of the mixing chamber. Themixing structure or device can be, for example, integrally formed withthe tool body or can be a separate component insertable into the toolbody. In one embodiment, the mixing structure or device is in the formof a Venturi device positioned within the mixing chamber.

The ignition tool can comprise a diffuser designed to control thecharacteristics of the mixture of gases leaving the outlet from the toolbody. Any suitable type of diffuser, such as a perforated plate, can beused.

The ignition tool can comprise flow deflectors extending from an outsidesurface of the tool body, for deflecting the flow of gas (such as theoxidant) away from a downstream region of the tool body, such that thedownstream region is not cooled by the flowing gas.

The ignition tool can comprise heat-exchange formations, such as fins orvanes extending from the tool body, for cooling the outlet from and/orinterior of the body.

The mixing chamber can be defined by the tool body and a diffuser plateextending transversely across the tool body adjacent the outlet from thebody.

The ignition tool can comprise a support for supporting the ignitionmeans or other component within the tool body or externally of the body.Any suitable type of support can be used. The support can be, forexample, integrally formed with the tool body or can be a separatecomponent insertable into the tool body. In one embodiment, the supportis in the form of a spacer sleeve or stay that snugly fits within thetool body and supports the ignition means within an interior region ofthe sleeve.

The ignition tool can comprise a non-return/check valve (ball andspring, spring loaded flapper valve or the like) to prevent ignitionfuel and product gas (syngas) reverse flow up a tube of the coiledtubing.

The coiled tubing can comprise a non-return/check valve (ball andspring, spring loaded flapper valve or the like) fitted within a tube toprevent product gas (syngas) reverse flow up the tube.

The ignition apparatus can comprise one or more sensors for sensing andreporting conditions in the ignition tool, adjacent the ignition tool,well channel and/or adjacent coal seam. Any suitable type of sensor canbe used. For example, the sensor can be a: thermocouple for sensing thetemperature in the well channel, coal seam or ignition tool etc; a gassensor for sensing the nature of the gas within the well/well channel; apressure sensor for sensing pressure within the well/well channel; anoptical sensor for viewing the well, well channel or coal seam; or aposition sensor for reporting the location of the ignition tool withinthe well/well channel. The sensor can be connected to the ignition toolouter body or housed within the tool body or coiled tubing or both. Anelectrical cable of the sensor can extend within the coiled tubing andinternally or externally of the tool body.

The ignition apparatus can comprise a controller operable to triggerignition, including the provision of electrical energy or ignition fuel,oxidant or the release of a combustible ignition chemical. Thecontroller can comprise a control cabinet. The controller can comprise apipe manifold in fluid communication with the coiled tubing and ignitionchemical, ignition fuel and oxidant sources.

The controller can be operable remotely from the ignition tool to (1)control the ignition fuel/ignition chemical and oxidant ratio of themixture, (2) monitor combustion of the mixture, and (3) control thesupply of electrical energy to the ignition. The controller can comprisea voltage and current measuring and controlling device connected to anelectrical ignition device by means of an electrical cable extendingthrough the coiled tubing.

The controller can consist of trim, non-return and isolation valves,flow measuring devices and pressure relief devices. Such operatingdevices can allow for injection rate measurement and control for oxidantand ignition fuel respectively. It can also allow purging of theignition fuel with inert gases such as nitrogen. Oxidant/ignition fuelmixture can be adjusted using flow controlling devices, such devicesbeing either pneumatically actuated, manually choked, quarter-turn typesor electrically actuated.

The controller can comprise pressure safety devices, filtration, flowmetering devices in addition to isolation valves. Control logic canallow the oxidant/ignition fuel to flow as per the required settings. Incase of power failure or loss of oxidant the control logic can stop flowof the ignition fuel.

The source of oxidant (eg. compressor for air or liquid or gaseousoxygen storage tank or generator etc), ignition fuel (eg. compressed gasor liquid cylinders etc.) and ignition chemical (eg. compressed gas orliquid cylinders etc.) can be connected to a pipe manifold of thecontroller and further to the coiled tubing and well head of theinjection well. A power supply (generator) can be electrically connectedto the controller and further to the electrical cable and sensor cableextending through the coiled tubing. The controller can be skid-mountedfor ease of transport.

The controller can supply electrical energy to the ignition tool to:ignite the ignition fuel/ignition chemical/oxidant mixture; monitor thecondition of the ignited mixture and ramping the oxidant flow as well asignition fuel gas up or down when re-igniting the mixture if theignition is extinguished before combustion is established in the coalseam; and, once ignition is sustained, ramp up the flows of ignitionfuel followed by oxidant or vice versa depending on the ratio attainedfor sustainable ignition, until combustion has been established in thecoal seam.

The controller controls the fuel/oxidant ratios to between the lowerflammability limit (LFL) of the fuel and the upper flammability limit(UFL) of the fuel. This ensures that not only can the gas mixture at theignition tool ignite but the flame is sustainable.

Once combustion has been established, the method according to theinvention further includes a step of maintaining the oxidant at a levelto support the combustion.

In order to continue the underground coal gasification process throughthe coal seam, it may be necessary to reposition the ignition tool to anew ignition site where the coal in the vicinity of the new ignitionsite can be ignited and a new combustion zone created to progress thecombustion along the coal seam and have optimum consumption of the coalresource. At the new combustion site the energy produced during thegasification process is also sufficient to maintain the temperaturewithin the new combustion zone at a level which supports the chemicalreactions taking place.

Thus to support particularly the movement of the combustion zone thecoiled tubing and ignition tool can be drawn along the coal seam andre-ignited periodically to not only maintain the combustion in thecombustion zone but also to initiate subsequent combustion zones in thecoal seam. Hence, the method according to the invention further includesa step of moving the ignition tool along the coal seam. While this ismost applicable to substantially horizontal bore holes/well channels,the invention may also be used with vertical or inclined boreholes orboreholes which have a combination of configurations.

Preferred embodiments of the invention will now be described, by way ofexample, with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts general features of an ignition apparatus configured toignite an underground coal seam, according to an embodiment of thepresent invention;

FIG. 2 depicts parts of ignition apparatuses (utilising single coiledtubing) for igniting an underground coal seam, according to embodimentsof the present invention;

FIG. 3 depicts parts of ignition apparatuses (utilising concentriccoiled tubing) for igniting an underground coal seam, according toembodiments of the present invention;

FIG. 4 depicts parts of ignition apparatuses (utilising single coiledtubing) for igniting an underground coal seam, according to embodimentsof the present invention;

FIG. 5 depicts part of an ignition apparatus (utilising single coiledtubing) for igniting an underground coal seam, according to anembodiment of the present invention;

FIG. 6 depicts part of an ignition apparatus (utilising single coiledtubing) for igniting an underground coal seam, according to anembodiment of the present invention;

FIG. 7 depicts part of an ignition apparatus (utilising single coiledtubing) for igniting an underground coal seam, according to anembodiment of the present invention;

FIG. 8 depicts part of an ignition apparatus (utilising single coiledtubing) for igniting an underground coal seam, according to anembodiment of the present invention;

FIG. 9 depicts part of an ignition apparatus (utilising single coiledtubing) for igniting an underground coal seam, according to anembodiment of the present invention;

FIG. 10 depicts part of an ignition apparatus (utilising concentriccoiled tubing) for igniting an underground coal seam, according to anembodiment of the present invention; and

FIG. 11 depicts part of an ignition apparatus (utilising concentriccoiled tubing) for igniting an underground coal seam, according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the figures, like reference numerals refer to like features.

Referring first to FIG. 1, there is generally depicted an ignitionapparatus 150 configured to ignite an underground coal seam 151. Thereis shown an injection well 152 having a well head 153 and a well channel154 extending from a heel of the well 152 through the coal seam 151.

The ignition apparatus 150 comprising an ignition system, a positioningsystem, a sensor 170 and a controller 165.

The ignition system comprises ignition means and an ignition tool 155for igniting the underground coal seam 151 from within the well channel154 (or well liner encasing the well channel 154).

The positioning system comprises coiled tubing 156 connected to theignition tool 155 and extendible through the well head 153 within thewell channel 154 to position the ignition tool 155 at a desired locationwithin the well channel 154. The positioning system further comprises aspool 157 for transporting and dispensing the coiled tubing 156.

The coiled tubing 156 of the positioning system can comprise a singletube (‘single coiled tubing’) or concentrically arranged inner and outertubes (‘concentric coiled tubing’), and an end of each tube is connectedto an end of the ignition tool 155 either directly or by way of anadaptor that is welded to the end of each tube and is usually eitherwelded or screwed to an end of the ignition tool 155. A preferreddiameter for the outer tube is two inches whereas a preferred diameterfor the inner tube is ¾ inches.

The coiled tubing 156 is also in fluid communication with pipes of amanifold 171 of the controller 165 by way of hoses 172 and further influid communication with sources of fluids 162, 163 (ignition chemical,ignition fuel and oxidant—as the case may be).

The single or outer tube of the coiled tubing 156 is used to conveyelectrical and/or sensor cables (eg. from a sensor/thermocouple 170)from the ignition tool 155 to the controller 165 via also electricallines 173 that extend from the spool 157.

The ignition means can directly ignite the coal seam 151 itself, orignite combustible fluid (gas, liquid) either resident in the wellchannel/well liner or supplied to the well channel/well liner as a gas,liquid or solid.

In one concentric coiled tubing embodiment, the ignition means comprisesan electrical spark generator 160 (eg. spark plug) electricallyconnected by an electric cable to a power supply (generator—not shown)for generating the spark. In another concentric coiled tubingembodiment, the ignition means comprises an electrical heat resistor(eg. glow plug) 160 electrically connected by an electric cable to apower supply (not shown) for electrifying the resistor. The resistorcan, for example, generate about 180 kW of heat. For both embodiments,the ignition means further comprises an ignition fuel source (compressedgas or liquid cylinders 162, eg. containing hydrocarbons such asmethane) and oxidant source (eg. air compressor 163) for fuelingcombustion. Ignition fuel is fed to the ignition tool 155 via the innertube of the coiled tubing 156 and oxidant is fed to the ignition tool155 via the outer tube of the coiled tubing 156. The electrical sparkgenerator/electrical heat resistor 160 is housed within the ignitiontool 155 (or possibly outside the ignition tool 155) and in the path ofthe mixture of combustible gases (ignition fuel and oxidant) that flowthrough the ignition tool 155. In a single coiled tubing embodiment,ignition fuel alone can flow through the tube to the ignition tool 155.

In yet another concentric coiled tubing embodiment the ignition meanscomprises at least one type of ignition chemical and ignition chemicalsource (eg. compressed gas or liquid cylinders 162). The ignitionchemical can be a pyrophoric substance—eg. a liquid such astriethylboron (TEB), a gas such as silane, solids such as phosphorus oralkali metal, a pyrophoric chemical and hydrocarbon mixture such as TEBvaporized in methane, or a pyrophoric chemical and an inert gas such asTEB and nitrogen. The hydrocarbon or inert gas flow can helptransport/vaporize the pyrophoric material or slugs/plug flows of thepyrophoric chemical to the ignition tool 155. The ignition means canfurther comprise an oxidant source (eg. air compressor 163) for fuelingignition and combustion. The ignition chemical specifically reacts withoxidant (air or oxygen) within the well channel or the coal seam itselfto ignite the coal seam.

The ignition chemical can be specifically released when the ignitiontool 155 is at the desired well/well channel location. The ignitionchemical can be fed to the ignition tool 155 from cylinders 162 via theinner tube whereas the oxidant can be fed to the ignition tool 155 fromthe air compressor 163 via the outer tube. In a single coiled tubingembodiment, ignition chemical alone can flow through the tube to theignition tool 155.

In a single coiled tubing embodiment the ignition means can comprisepure oxygen or substantially pure oxygen (cylinders 162) fed through thetube of the coiled tubing and ignition tool 155. The oxygen ignites thecoal seam directly. The ignition means can further comprise an oxidantsource (air compressor 163) for fueling combustion.

To generalize, for ignition apparatus comprising single coiled tubing,oxidant injected into the well channel may flow externally of the tubeof the coiled tubing. Also for ignition apparatus comprising singlecoiled tubing, ignition fuel and/or ignition chemical injected into thewell channel may flow within the tube. For ignition apparatus comprisingconcentric tubes, oxidant injected into the well channel may flow withinthe outer tube (preferably as well as in the well channel itselfexternally of the outer tube) and ignition fuel/ignition chemical mayflow within the inner tube.

If using a single coiled tubing (having a single tube) or concentriccoiled tubing (having inner and outer tubes), the (outer) tube can bemade of stainless steel or carbon steel. If air is used as the oxidant,the outer tube can be made of carbon steel and the inner tube can bemade of copper. If air or oxygen is used as the oxidant, the outer tubecan be made of stainless steel and the inner tube can be made of copperor stainless steel.

The ignition tool 155 can be made chiefly of stainless steel or carbonsteel. Sacrificial pieces of the ignition tool, such as a blow-out plug(as described later), can be made of heat intolerant materials such asaluminum, plastics material or rubber. The ignition tool or the toolbody can have any suitable outer diameter and length. For example, theignition tool or the tool body can have an outer diameter of about 2inches, 3 inches or 4 inches, for example. Preferably the ignition toolor the tool body has a diameter of about 2 inches.

The controller 165 (skid) is operable to trigger ignition, including theprovision of electrical energy or ignition fuel, oxidant or the releaseof a combustible ignition chemical. The controller 165 comprises acontrol cabinet 169. The controller 165 comprises a pipe manifold 171 influid communication with the coiled tubing 156 and ignition chemical,ignition fuel and oxidant sources 162, 163.

The controller 165 further comprises trim, non-return and isolationvalves, flow measuring devices and pressure relief devices. Suchoperating devices allow for injection rate measurement and control foroxidant and ignition fuel gases respectively. It also allows purging ofthe ignition fuel gases with inert gases such as nitrogen.Oxidant/ignition fuel mixture can be adjusted using flow controllingdevices, such devices being either pneumatically actuated, manuallychoked, quarter-turn types or electrically actuated. The controller 165comprises pressure safety devices, filtration, flow metering devices inaddition to isolation valves. Control logic allows the oxidant/ignitionfuel gas to flow as per the required settings. In case of power failureor loss of oxidant the control logic slams shut the ignition fuel gas.The controller 165 enables the use of volatile chemicals such as TEB,silane or mixture of any kind.

The controller can maintain the ratio of the oxidant gas and ignitionfuel between predetermined limits which are preferably the upperflammability limit and the lower flammability limit for the ignitionfuel and works on the basis of the stoichiometric ratio of oxidant toignition fuel.

The controller is configured to supply power to the electrical ignitiondevice when the fuel ratio is between the lower flammability limit andupper flammability limit. The thermocouple on the ignition toolindicates that no flame is present, and a flame is required to eithermaintain or initiate combustion at the ignition site.

The supply of power and temperature sensing for the monitoring systemare managed through multi-core electrical cable extending within thetube to the ignition tool. The temperature monitoring system indicatesvia the thermocouple fixed at the ignition tool whether the ignition issuccessful and further confirms the presence of the flame within thecombustion zone of coal seam.

The ignition is sustained by the supply of ignition fuel and oxidantwith the fuel gas ratio being controlled from above ground. Appropriateadjustment to the oxidant to fuel ratio is made depending onconfirmation of the coal ignition at the coal seam. Preferably the ratiois maintained close to the lower flammability limit of the fuel gas toensure sufficient oxidant is provided to initiate combustion within thecombustion zone. Once ignition has taken place, the combustion gases aswell as any volatile gases emanating from the coal seam are pushed outfrom an end of the well (ie. production well) and routed to a flare. Theproduct gas (syngas) quality is monitored and once the coal in thecombustion zone is confirmed as having been ignited and combustionmaintained, the ignition fuel to the ignition tool is cut back graduallyuntil only oxidant is provided to the combustion zone. The coiled tubingcan then be retracted from the bore hole/well and the supply of oxidantcan be increased up to the supply required for full coal gasificationproduction conditions.

Ignition of the coal seam can take place at any predefined ignitionpoints. This enables further re-ignition of the coal seam by simplyretracting the ignition tool along the coal seam and reinitiating theignition process. This can be done either when the combustion process inan earlier combustion zone has been completed or while the undergroundcoal gasification is taking place in other positions along the coalseam. The ability to retract and reignite the coal seam is advantageousin that it has the ability to reduce underground gasification costs byenabling much longer stretches of horizontal bore hole/well channelwithin the seam to be ignited. This enables the combustion in the coalseam to be supported for a longer time thereby increasing the wellproduction life and amortizing the cost over a longer period ofproduction.

In order to install the ignition apparatus, the ignition tool togetherwith the coiled tubing are inserted into the bore hole/well which islined with a casing. The casing extends at least to the section of thebore hole/well channel which is substantially horizontal, inclined orvertical within the coal seam. The ignition tool is first fitted to thetip of the coiled tubing together with cables running within thetube/tubes. The ignition tool together with the coiled tubing areinserted into the bore hole/well and positioned at a predefined locationor ignition site within the coal seam. The ignition fuel and oxidant aresupplied through the coiled tubing and the space/void between the tubingand the bore hole casing at a predefined rate. This rate is determinedby the required oxidant to ignition fuel ratio and the heat required toignite the coal seam. Once the ignition fuel and oxidant have reachedthe ignition tool, the electrical ignition device is energized to ignitethe ignition fuel and oxidant at the ignition tool.

The apparatus allows ignition of the coal seam to take place at anypredefined ignition points. This enables further re-ignition of the coalseam by simply retracting the ignition tool along the coal seam andreinitiating the ignition process. This can be done either when thecombustion process in an earlier combustion zone has been completed orwhile the underground coal gasification is taking place in otherpositions along the coal seam.

Further depictions of various single coiled tubing embodiments are shownin FIG. 2.

FIG. 2 generally depicts parts of ignition apparatuses 110 (110 a, b, c)for igniting an underground coal seam 111 from within a well channel 112(shown encased in a well liner) that extends through the seam 111. Eachignition apparatus 110 comprises an ignition system comprising ignitionmeans and an ignition tool 113 (113 a, b, c) for igniting theunderground coal seam 111 from within the well channel 112.

Each ignition apparatus 110 further comprises a positioning systemcomprising coiled tubing 114 (114 a, b, c) connected to the ignitiontool 113 and extendible within the well channel 112 to position theignition tool 113 at a desired location within the well channel 112.Other components of each apparatus 110 not shown in FIG. 2 can begleaned from FIG. 1.

The positioning system includes coiled tubing 114 comprising a singletube 114 and an end of the tube 114 is connected to an end of theignition tool 113 either directly or by way of an adaptor. For coiledtubing 114 comprising a single tube 114, oxidant will normally beinjected into a well and flow on the outside of the coiled tubing/tube114 but within the well channel 112.

As explained previously, the ignition apparatuses 110 can have variousignition means.

In FIG. 2 (a) the ignition means includes an electrical heater (glowplug) 116 and an electrical cable 117 extends from the heater 116through the tube 114 a to the surface to a power controller. Ignitionfuel (eg. hydrocarbon, such as methane) is fed from an above groundsource through the tube 114 a and through the ignition tool 113 a to theelectrical heater 116 for ignition and for further combustion with theoxidant within the well channel 112 so as to ignite the coal seam 111.

In FIG. 2 (b) the ignition means includes an ignition chemical 117 (eg.pyrophoric gas) that is fed from an above ground source through the tube114 b and completely through the ignition tool 113 b where upon mixingwith the oxidant it ignites the coal seam 111.

In FIG. 2 (c) the ignition means includes an electrical heater 118 andan electrical cable 119 extends from the heater 118 through the tube 114c to the surface to a power controller. When energised, the heater 118ignites the oxidant and coal seam 111. In this embodiment, no gas flowoccurs through the tube 114 c. Rather, the tube 114 c merely conveys theelectrical cable 119.

FIG. 3 generally depicts parts of ignition apparatuses 120 (120 a, b, c)for igniting an underground coal seam 121 from within a well channel 122(shown encased in a well liner) that extends through the seam 121. Eachignition apparatus 120 comprises an ignition system comprising ignitionmeans and an ignition tool 123 (123 a, b, c) for igniting theunderground coal seam 121 from within the well channel 122.

Each ignition apparatus 120 further comprises a positioning systemcomprising coiled tubing 124 (124 a, b, c) connected to the ignitiontool 123 and extendible within the well channel 122 to position theignition tool 123 at a desired location within the well channel 122.Other components of each apparatus 120 can be gleaned from FIG. 1.

The positioning system includes coiled tubing 124 comprising dualconcentrically arranged tubes and an end of each tube is connected to anend of the ignition tool 123 either directly or by way of an adaptor. Aninner tube 125 (125 a, b, c) extends within an outer tube 126 (126 a, b,c).

For concentric coiled tubing 124, ignition fuel (such as the hydrocarbongas methane) and/or ignition chemical (such as pyrophoric gas) isnormally fed from an above ground source through the inner tube 125 andthrough the ignition tool 123. Oxidant (such as air or oxygen) isnormally fed from an above ground source through the outer tube 126 andthrough the ignition tool 123. Oxidant can also be fed from an aboveground source externally of the outer tube 126 but within the wellchannel 122.

As explained previously, the ignition apparatuses 120 can have variousignition means.

In FIG. 3 (a) the ignition means includes an ignition device 130 a inthe nature of an electrical heater (glow plug) or spark generator (sparkplug) and an electrical cable 131 extends from the device 130 throughthe outer tube 126 a to a power controller. Ignition fuel is fed from anabove ground source through the inner tube 125 a and to an inlet pipe133 of the ignition device 130. Oxidant is fed from an above groundsource through the outer tube 126 a to the ignition device 130 whereuponit mixes with the ignition fuel. After mixing, igniting and passingthrough a diffuser plate 132 of the ignition tool 123 a, the flameignites the coal seam 121.

In FIG. 3 (b) the ignition means includes an ignition chemical 135 (eg.pyrophoric gas) that is fed from an above ground source through theinner tube 125 b and to an inlet pipe 135 of the ignition tool 123 b.Oxidant is fed from an above ground source through the outer tube 126 b(as well as within the well externally of the outer tube 126 b) to theignition tool 123 b. Upon leaving the tool 123 b, the oxidant mixes withthe ignition chemical and ignites the coal seam 121.

In FIG. 3 (c) the ignition means includes an ignition device 140 in thenature of an electrical heater (glow plug) or spark generator (sparkplug) and an electrical cable 141 extends from the device 140 throughthe outer tube 126 c to a power controller. Ignition fuel is fed from anabove ground source through the inner tube 125 c and out a spray nozzle141 to the ignition device 140. Oxidant is fed from an above groundsource through the outer tube 126 c to the ignition device 140. Prior tobeing ignited by the ignition device 140, the gases pass through amixing chamber 142 containing a Venturi device 143 and are thoroughlymixed. After mixing, igniting and passing through a diffuser plate 147of the ignition tool 123 c, the flame is exposed to a further source ofoxidant and ignites the coal seam 121.

Yet further examples of ignition apparatuses 200 (200 a, b, c, d)comprising concentrically arranged tubes/coiled tubing 201 (201 a, b, c,d) connected to ignition tools 202 (202 a, b, c, d) are shown in FIG. 4.In each case the ignition means includes an electrical ignition device203 (203 a, b, c, d) in the nature of an electrical heater (glow plug)or spark generator (spark plug) and an electrical cable 204 (204 a, b,c, d) extends from the device 203 through an outer tube 205 (205 a, b,c, d) to the surface to a power controller. Ignition fuel or ignitionchemical (gas) is fed from an above ground source through an inner tube206 (206 a, b, c, d) and to the ignition device 203 via an inlet pipe218 (218 a, b, c, d) of the ignition tool 202. Oxidant (gas) is fed froman above ground source through the outer tube 205 to the ignition device203.

Each ignition apparatus 200 also has a sensor/thermocouple 210 (210 a,b, c, d), a cable of which extends through the outer tube 205. Althoughnot completely labeled, each ignition tool 202 comprises various toolbody pieces that are screwed to one another and further welded to thecoiled tubing 201. Body piece 219 (219 a, b, c, d) is a coiled tubingadapter.

Prior to being ignited by the ignition device 203, the gases passthrough various types of mixing chambers 211 (211 a, b, c, d). Theignition tool 202 a of FIG. 4 (a) has a mixing chamber 211 a containinga spiral baffle or baffles 213. The ignition tool 202 b of FIG. 4 (b)has a mixing chamber 211 b containing a diffuser plate 214. The ignitiontool 202 c of FIG. 4 (c) has a mixing chamber 211 c containing a Venturidevice 216. The ignition tool 202 d of FIG. 4 (d) has a mixing chamber211 d containing a diffuser plate 217 and mixing is further assisted inthat an inlet pipe 218 of the ignition tool 202 d ends with a spraynozzle.

After mixing, igniting and exiting the ignition tool 202, the flame isexposed to a further source of oxidant and ignites the coal seam.

Yet further examples of ignition apparatuses comprising singletubes/single coiled tubing connected to ignition tools are shown in FIG.5-7.

Referring now to FIG. 5, there is shown an ignition apparatus 301 forigniting an underground coal seam 302. The ignition apparatus 301comprises an ignition system comprising ignition means and an ignitiontool 304 for igniting the underground coal seam 302 from within the wellchannel 303. The ignition apparatus 301 further comprises a positioningsystem comprising coiled tubing 305 connected to the ignition tool 304and extendible within the well channel 303 to position the ignition tool304 at a desired location within the well channel 303. The ignitionapparatus 301 can have other components as generally shown in FIG. 1.

The coiled tubing 305 comprises a single tube 306 (stainless steel orcarbon steel) and an end of the tube 306 is threaded 307. The coiledtubing 305 further comprises heat-exchange fins 310 extending from thetube 306. These fins 310 keep the tube 306 interior cool (to protect theelectrical cable 311 of the ignition means that extends through the tube306). These fins 310 also help centralise the ignition tool 304 withinthe well channel 303.

The ignition tool 304 includes a tool body 308 having an inlet end 309that is threaded and connected to the threaded end 307 of the tube 306.This connection need not be a threaded one. Alternatively, the tube 306and body 308 could be welded together. The body 308 is made of highmelting point and oxidation resistant metal such as stainless steel,inconel, monel or hastelloy.

The ignition means comprises an electrical ignition device 312electrically connected to an above-ground power supply (not shown) withthe cable 311. The device 312 includes an electrical heating element 313wound around a non-conductive (ceramic) core 314. The device 312includes two non-conductive (ceramic) spacers 315, 316 that position theheating element 313 within the body 308. Wires (not labeled) of theheating element 313 extend through spacer 315 and contact the cable 311.

The ignition tool 304 includes a flow diverter protrusion 317 thatdiverts the flow of oxidant away from a heating element 313 end of thebody 308, as shown by the arrows. The spacer 313 shields the electricalcable 311 and prevents it from melting and being destroyed.

The ignition apparatus 301 further comprises a thermocouple 319 thatextends from within the tube 306 and part way into the tool body 308.The thermocouple 319 is used to determine whether heating element 313reaches its intended temperature as well as to keep a watch on thetemperature of the cable 311 so that it does not get destroyed.

A trip condition (of the power supply to the heating element 313) can beconfigured at the surface once the thermocouple 319 at the electricalcable 311 indicates the electrical cable 311 is operating above itsdesign temperature. The electrical cable 311 is protected by having airflow around the tube 306. This is further enhanced by the heat-exchangefins 310 that provide a bigger surface area for cooling with theaddition of a conductive paste to improve contact between the tube 306and electrical cable 311.

In use, the heating element 313 heats up the body 308 and radiates thisheat 320 onto the coal seam surface 302 until the coal reaches itsauto-ignition temperature in the presence of oxidant and results in thecombustion of the coal. The flow diverter 317 diverts the flow ofoxidant away from the heating element 313 containing end of the body308, as shown by the arrows and therefore prevents excessive cooling ofthe heating element 313 containing end of the body 308.

Referring now to FIG. 6, there is shown another type of ignitionapparatus 331. The ignition apparatus 331 comprises an ignition systemcomprising ignition means and an ignition tool 334 for igniting theunderground coal seam 332. The ignition apparatus 331 further comprisesa positioning system comprising coiled tubing 335 connected to theignition tool 334 and extendible within the well channel 333 to positionthe ignition tool 334 at a desired location within the well channel 33.The ignition apparatus 331 can have other components as generally shownin FIG. 1.

The coiled tubing 335 comprising a single tube 336 (stainless steel orcarbon steel) and an end of the tube 336 is threaded 337. The coiledtubing 335 further comprises positioning fins 340 to help centralise theignition tool 334 within the well channel 333.

The coiled tubing 336 further comprises a non-return/check valve 345(ball and spring, spring loaded flapper valve or the like) fitted withinthe tube 336, to prevent product gas/syngas reverse flow up the tube 336when removing the coiled tubing 335 from the well channel 333.

The ignition tool 334 includes a body 338 having an inlet end 339(having inlet 339) that is threaded and connected to the threaded end337 of the tube 336 in a fluid-tight manner. This inlet end 339connection need not be a threaded one. Alternatively, the tube 336 andbody 338 could be welded together in a fluid-tight manner.

The tool body 338 further has an outlet end 341 (having outlet 341). Theoutlet 341 is of reduced diameter relative to the inlet 339. The outletend 341 of the body 338 is in the form of a blow-out plug 342 that isconnected to a remainder of the body 338. The blow-out plug 342 has astem around which extends an o-ring 343 and the o-ring 343 friction fitswithin the outlet 341. The blow-out plug 342 can be made of aluminium orcan alternatively be fabricated from durable rubber or plastic. Thisblow-out plug 342 material will be consumed within the gasifier due tothe high temperatures present. The tool body 338 is chiefly made of highmelting point and oxidation resistant metal such as stainless steel,inconel, monel or hastelloy.

The tube 336 can convey ignition chemical to the inlet 339 of theignition tool 334 and the tool body 338 provides a passage 344 forconveying ignition chemical from the tube 336 to the outlet 341.

The ignition apparatus 331 can further include a thermocouple attachedto the tube 336 and/or tool body 338 (not shown). Although not shown,the ignition apparatus 331 can further comprise a source of oxidant asmentioned in respect of FIG. 1.

Although not shown, the ignition apparatus 331 can further comprise asource of ignition chemical connected to the tube 336 in a fluid-tightmanner. The ignition chemical can be a pyrophoric chemical (eg. a liquidsuch as TEB, a gas such as silane, solids such as phosphorus or alkalimetal), or a pyrophoric chemical and hydrocarbon mixture (e.g. TEBvaporized in methane), or a pyrophoric chemical and an inert gas (e.g.TEB and nitrogen). The hydrocarbon or inert gas flow 347 can helptransport/vaporize the pyrophoric chemical or slugs/plug flows 346 ofthe pyrophoric chemical to the ignition tool 334.

Although not shown, the ignition apparatus 331 comprises a controlleroperable to trigger ignition. The controller controls the flow ofignition chemical etc. into the tube 335 and well as the flow of oxidantinto the well—as generally described for FIG. 1.

In use, the pyrophoric chemical provides the heat for ignition oralternatively the initial flame for the hydrocarbon material mixed withit or following it in a plug flow 346 to sustain the flame until thecoal is ignited. The inert gas 347 can be used to either transport thepyrophoric chemical 346 through the tube 336 or can be used to inert thetube 336 before starting the ignition process and after ignition beforethe coiled tubing 335 is removed from the well channel 333.

Injected oxidant around the ignition tool 334 provides the oxidant tosustain the ignition when the oxidant and pyrophoric chemical mixturecome into contact with each other at the outlet end 341 of the tool body338. The heat generated by the oxidant and pyrophoric chemical/mixtureexothermic chemical reaction provides heat to the coal surface 332 toheat the coal up until the coal combusts at temperatures exceeding theauto-ignition temperature of the coal.

The reduced diameter outlet 341 enables a higher exit velocity of thepyrophoric chemical/mixture to project the flame away from the coiledtubing 335 and prevent excessive heat at the body outlet end 341.

The ignition tool 334 can be engineered with a finned profile on anouter circumference of the body 338 so as to provide a largerheat-exchange surface for enhanced cooling of the body 338 from theinjection oxidant flow down the injection well annulus, around theignition tool 334.

The blow-out plug 342 prevents coal dust, drilling mud or water fromentering the ignition tool 334 when inserted down hole and past the wellcasing 348. The blow-out plug 342 is pushed out of engagement with theoutlet 341 by the pressurized flow of the pyrophoric chemical/mixture orinert gas.

Referring now to FIG. 7, there is shown an ignition apparatus 351 forigniting an underground coal seam 352 from within a well channel 353that extends through the seam 352. The ignition apparatus 351 comprisesan ignition system comprising ignition means and an ignition tool 354for igniting the underground coal seam 352. The ignition apparatus 351further comprises a positioning system comprising coiled tubing 355connected to the ignition tool 354 and extendible within the wellchannel 353 to position the ignition tool 354 at a desired locationwithin the well channel 353. The ignition apparatus 351 can have othercomponents as generally shown in FIG. 1.

The positioning system includes coiled tubing 355 comprising a singletube 356 (stainless steel or carbon steel) and an end of the tube 356 isthreaded 357.

The ignition tool 354 includes a body 358 having an inlet end 359(having inlet 359) that is also threaded and connected to the threadedend 357 of the tube 356 in a fluid-tight manner. This inlet endconnection need not be a threaded one.

The tool body 358 further has an outlet end 361 (having outlet 361) thatextends to the inlet 359 by way of a passage 364. The outlet end 361 ofthe body 358 is in the form of a blow-out plug 362 that is connected toa remainder of the body 358. The blow-out plug 362 has a stem aroundwhich extends an o-ring 363 and o-ring 363 friction fits with the outlet361, as described for FIG. 6.

The tube 356 can convey ignition fuel 372 such as methane to the inlet359 of the ignition tool 354 and the passage 364 conveying the ignitionfuel 372 from the inlet 359 to the outlet 361.

The ignition tool 354 comprises a gas mixing (turbulence-creating)chamber 370 located within the body 358 within which the oxidant andignition fuel mix. The body 358 provides a wall of the chamber 370 and adiffuser plate 371 extending across the body 358 defines a downstreamend of the chamber 370. The mixing chamber 370 includes an upstreamVenturi device 372. The ignition tool 354 comprises oxidant intakes 373in the body 358 through which oxidant may be drawn by way of thepressure differential caused by the Venturi device 372.

The ignition tool 354 further comprises a non-return/check valve 365(ball and spring, spring loaded flapper valve or the like) fitted withinthe passage 364 to prevent ignition fuel and product gas (syngas)reverse flow up the tube 356.

The body 358 comprises four body pieces that are connectable end to end,such that the ignition tool 354 can be readily assembled from itscomponents. Three of the body pieces are threaded and the fourth is thefriction-fitted blow-out plug 362.

The ignition means comprises an electrical ignition device 366electrically connected to an above-ground power supply (not shown) withcable 367 that, when electrified, heats up or sparks. The ignitiondevice 366 can comprise dual glow plugs, each having a heating elementlocated at a respective tip of a ceramic body. Alternatively, theignition device 366 could be a spark generator (spark plug) thatgenerates sparks when electrified. However, an advantage of a glowplug-type device is that lower voltage is needed and there is aconsiderable drop in voltage over the distance from above ground to thecoal seam.

The electrical ignition device 366 is connected to an external surfaceof the tool body 358. The electrical cable 367 extends from theelectrical ignition device 366 along the body 358, through a fluid-tightport 374 into the passage 364 and further through the tube 356 to thepower supply.

The ignition apparatus 351 has a thermocouple 369 attached the externalsurface of the body 358 for measuring the temperature at the outlet 361.A signal cable (not labelled) of the thermocouple 369 extends throughthe port 374 and further through the tube 356. The thermocouple 369 isused to determine whether the ignition tool 354 reaches the correcttemperature. Compression fittings (not shown) around the cable 367 andthe thermocouple cable tighten the electrical cables 367 and provideport 374 with a pressure-tight seal.

The ignition tool 354 further comprises positioning fins 360 extendingfrom the body 358. These fins 360 protect the electrical/signal cables367 and the ignition device 366 from damage when running the tool 354down hole. These fins 360 help centralise the tool body 358 within thewell channel 353.

Although not shown, the ignition apparatus can further comprise a sourceof oxidant as described for FIG. 1. Although not shown, the ignitionapparatus 351 comprises a controller operable to trigger ignition, asgenerally described for FIG. 1.

In use, ignition fuel (hydrocarbon gas, preferably methane) is fedthrough the tube 356 to the tool inlet 359, following which the gasflows through the non-return check valve 365 and further through theVenturi device 372. The Venturi device 372 is sized to create a pressuredifferential required such that oxidant surrounding the ignition tool354 is drawn into the body's passage 364 to mix with the ignition fuelin the mixing chamber 370 downstream of the Venturi device 372. Thehigher the ignition fuel flow, the greater the pressure drop across theVenturi device 372, the more oxidant is sucked in to achieve thestoichiometric ratio of oxidant to ignition fuel (in the range of 5:1 to20:1). From here the ignition fuel and oxidant mixture flows through thediffuser plate 371 where it is ignited by the ignition device 366 toproduce a flame so as to combust the coal seam 352.

Referring now to FIG. 8, there is shown an ignition apparatus 381 forigniting an underground coal seam 382 from within a well channel 383that extends through the seam 382. The ignition apparatus 381 comprisesan ignition system comprising ignition means and an ignition tool 384for igniting the underground coal seam 382 from within the well channel383. The ignition apparatus 381 further comprises a positioning systemcomprising coiled tubing 385 connected to the ignition tool 384 andextendible within the well channel 383 to position the ignition tool 384at a desired location within the well channel 383. The ignitionapparatus 381 can have other components as generally shown in FIG. 1.

The positioning system includes coiled tubing 385 comprising a singletube 386 (stainless steel or carbon steel) and an end of the tube 386 isthreaded 387. The ignition tool 384 includes a body 388 having an inletend 389 (having inlet 389) that is also threaded and connected to thethreaded end 387 of the tube 386 in a fluid-tight manner. This inlet endconnection need not be a threaded one.

The tool body 388 further has an outlet end 391 (outlet 391). The outletend 391 of the body 388 is in the form of a blow-out plug 392 that isconnected to a remainder of the body 388, as described for the earlierfigures.

The tube 386 can convey a pneumatic gas such as air 393 to the inlet 389of the ignition tool 384 and the tool body 388 has a passage 394 forconveying the pneumatic gas 393 from the tube 386 to the outlet 391.

The ignition means comprises a turbine coupled with a transformer 397located within the body 388 through which the pneumatic gas flows. Theignition means further comprises a pneumatic air supply, such as an aircompressor, connected to the tube 386. The ignition means also comprisesan electrical ignition device 400 electrically coupled to thetransformer 397. When electrified by the transformer 397, the device 400heats up.

The electrical heating device 400 includes an electrical heating element401 wound around a non-conductive piece of the tool body 388. Theignition tool 384 comprises protective positioning fins 402, 403 thatextend from the body 338.

The ignition tool 384 further comprises a non-return/check valve 395(Baal and spring type, cone and spring type, flapper with spring type orthe like) fitted within the passage 394 upstream of the turbine andtransformer 384 to prevent pneumatic gas and product gas (syngas)reverse flow up the tube 386.

The body 388 comprises body pieces that are connectable end to end, suchthat the ignition tool 384 can be readily assembled from its components.The body pieces are threaded, apart from the friction-fitted blow-outplug 392.

Although not shown, the ignition apparatus 381 can comprise athermocouple for monitoring the temperature adjacent the outlet 391.Although not shown, the ignition apparatus can further comprise a sourceof oxidant.

In use, pneumatic gas 393 such as air is fed through the tube 386 andcheck valve 395 and into the turbine and transformer 384 to generateelectrical power to energise the heating element 400 so as to ignite thecoal seam 382. The air drives the turbine 384 to generate electricalcurrent, which can then be altered to higher voltage by the transformer387.

The remainder of the air flows out of the body outlet 391 and into thewell channel 383 and cools the outlet 391.

The heating element 401 is fitted on the outside of the tool body 388and can be a separate threaded piece if it is deemed disposable, sincethe heating element 401 is installed on the outside of the tool body388.

Protective fins 402, 403 shield the heating element 401 from damage. Theheating element 401 can be coated in a wax layer to protect it frommoisture when being run down hole. Alternatively, a burn-away sheath canbe installed to protect against moisture.

The heating element 401 will heat up the coal seam 382 to above itsauto-ignition temperature and as a result ignite the coal in thepresence of the oxidant flow around the tool 384.

Referring now to FIG. 9, there is shown an ignition tool 22 of anignition apparatus, like that of FIG. 5.

The ignition tool 22 includes a tool body 23 having an inlet end 24 (fora power cable 29) welded to an end of a tube of single coiled tubing 21.

Ignition means of the ignition apparatus comprises an electricalignition device 25 electrically connected to an above-ground powersupply (not shown) with a power cable 29. The device 25 includes aseries of electrical heating elements 26 spaced around a non-conductivecore 27. Spacers 30, 31 are positioned each end of the core 27.

In use, the heating elements 26 heat up the body 23 and the bodyradiates this heat onto the coal seam surface until the coal reaches itsauto-ignition temperature in the presence of oxidant and results in thecombustion of the coal.

Referring now to FIG. 10 there is shown part of an ignition apparatus 1for igniting an underground coal seam. The ignition apparatus 1 has anignition tool 2 and concentric coiled tubing 3 that is very similar tothat shown in FIG. 3( c). Other non-illustrated components of theignition apparatus 1 are as generally described for FIG. 1.

The ignition tool 2 comprises a body 4, an ignition device 5, anignition device support 6, and a mixing chamber 7.

The ignition tool 2 has separate inlets for oxidant 8 and ignition fuel9 at one end of the body 4 that is connected to concentric tubes 10, 11of the coiled tubing 3, and an outlet 12 for ignited fuel at an opposingend of the body 4.

The body 4 comprises various body pieces (not labeled) that areconnectable end to end, such that the ignition tool 2 can be readilyassembled from its components.

The outlet end 12 of the body is tapered and in the form of a blow-outplug 25 (essentially as described earlier). The inlet end 8, 9 of thebody 4 is welded to the coiled tubing 3.

The ignition device 5 is an electrical heat resistor electricallycoupled by way of a cable 26 to a power source that, when electrified,heats due to its electrical resistance. The ignition device 5 comprisesdual glow plugs 13, each having a heating element located at arespective tip of a ceramic body. The glow plugs can, for example,generate about 180 kW of heat. Alternatively, the ignition device 5could equally be a spark generator that generates sparks whenelectrified. The electric cable 26 extends from the power source to theignition device 5 through the outer tube 10.

The ignition device support 6 comprises a spacer sleeve. This support 6fits snugly within the body 4. The ceramic body of the ignition device 5is supported by and extends from within the sleeve 6 and further throughopenings in a diffuser plate 15 that extends across the body 4, such theglow plug tip heating elements are located immediately adjacent theoutlet 12 of the body 4.

The ignition tool 2 comprises a gas mixing (turbulence-creating) chamber7 located within the body 4 within which the oxidant and the ignitionfuel mix. The body 4 provides a wall of the chamber 7 and the diffuserplate 15 defines a downstream end of the chamber 7. The mixing chamber 7includes a Venturi device 17 for creating back pressure. The Venturidevice 17 is in the form of a cylindrical insert that snugly fits withinthe body 4.

The ignition apparatus 1 further comprises a temperaturesensor/thermocouple 18 located within the body 4 adjacent the ignitiondevice 5. An electrical cable of the thermocouple 18 extends within theouter tube 10.

The inner tube 11 feeds ignition fuel such as methane, propane, butaneor mixtures thereof (or another type of volatile hydrocarbon gas) to themixing chamber 7. The outer tube 10 feeds oxidant such as air oroxygen-enriched air or substantially pure oxygen (20 to approximately100% oxygen) also to the mixing chamber 7.

The oxygen and ignition fuel first contact one another within the mixingchamber 7. The Venturi device 17 ensures that these gases mix prior totraveling through the spacer sleeve 6 and diffuser plate 15 to theheating elements of the glow plugs. When electrified, the heatingelements cause the gas mixture to ignite and the ignited gas mixturethen exits the body 4 via the outlet 12.

Referring now to FIG. 11, there is shown part of an ignition apparatusfor igniting an underground coal seam. The ignition apparatus has anignition tool 30 and concentric coiled tubing (not shown) that is verysimilar to that shown in FIG. 3( b). Other non-illustrated components ofthe ignition apparatus are as generally described for FIGS. 1 and 3( b).

The ignition apparatus comprises an ignition system comprising ignitionmeans and the ignition tool 30 for igniting the underground coal seamfrom within the well channel. The ignition apparatus comprises athermocouple 42 for monitoring temperature. Although not shown, theignition apparatus can further comprise a source of oxidant and ignitionchemical.

The coiled tubing comprises dual concentrically arranged tubes and anend of each tube is connected to the inlet end of the ignition tool 30either directly or by way of an adaptor (but usually by welding). Aninner tube extends within the outer tube.

A cable of the thermocouple 42 together with an electrical cable 41 (butnon-operational in this embodiment) extend through the outer tube.

The ignition tool 31 has a body 32 having an inlet end 33 and an outletend 34. The inlet end 33 has an inlet pipe 35 for receiving ignitionchemical and a second inlet 36 adjacent the inlet pipe 35 for receivingoxidant. The outlet end 34 of the body 32 is in the form of a blow-offcap 37 that, when removed, exposes pipe 35 to a well channel.

The ignition means includes an ignition chemical, eg. pyrophoric gas,(and possibly ignition fuel, eg. methane) that is fed from an aboveground source through the inner tube which is further fed to pipe 35.Oxidant is fed from an above ground source through the outer tube (aswell as within the well externally of the outer tube 33) and further tothe inlet 36 of the ignition tool 30.

The ignition tool comprises an o-ring/sleeve 43 that extends between thebody 32 and pipe 35, and keeps the pipe 35 centralised.

Oxidant flowing within the body 32 from the inlet 36 exits via an outlet50 created when the blow-off cap 34 is removed. Ignition chemicalflowing within the pipe 35 exits via an outlet 51 created when theblow-off cap 34 is removed. It is at this point that the oxidant mixeswith the ignition chemical and ignites the coal seam.

After the cap 34 has been removed from a remainder of the body 32, theignition tool 30 resembles the tool shown in FIG. 3( b).

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or figures.All of these different combinations constitute various alternativeaspects of the invention.

As used herein, except where the context requires otherwise, the term“comprise” and variations of the term, such as “comprising”, “comprises”and “comprised”, are not intended to exclude further additives,components, integers or steps.

Reference to any prior art in the specification is not, and should notbe taken as, an acknowledgment or any form of suggestion that this priorart forms part of the common general knowledge in Australia or any otherjurisdiction.

1. An ignition apparatus for igniting an underground coal seam fromwithin a well channel that extends through the seam, said apparatuscomprising: an ignition system comprising ignition means and an ignitiontool for igniting the underground coal seam from within the wellchannel; and a positioning system comprising coiled tubing connected tothe ignition tool and extendible within the well channel to position theignition tool at a desired location within the well channel.
 2. Theignition apparatus of claim 1, wherein the ignition means comprises anelectrical spark generator and a power supply for generating the spark.3. The ignition apparatus of claim 1, wherein the ignition meanscomprises an electrical heat resistor and a power supply forelectrifying the resistor.
 4. The ignition apparatus of claim 1, whereinthe ignition means comprises at least one type of ignition chemical,such as a pyrophoric substance.
 5. The ignition apparatus of claim 1,wherein the ignition means comprises pure oxygen or substantially pureoxygen that ignites the coal seam directly.
 6. The ignition apparatus ofany one of the preceding claims, wherein the ignition tool is connectedto the coiled tubing in a fluid-tight manner.
 7. The ignition apparatusof claim 6, wherein the ignition tool is connected to the coiled tubingby way of a screw thread or weld.
 8. The ignition apparatus of any oneof the preceding claims, wherein the ignition tool comprises a tool bodyhaving an inlet end connected to the coiled tubing.
 9. The ignitionapparatus of any one of the preceding claims, wherein the coiled tubingcomprises a single tube connected to the tool body.
 10. The ignitionapparatus of any one of claims 1 to 9, wherein the coiled tubingcomprises an inner tube extending within an outer tube, and one or bothof the inner and outer tubes are connected to the tool body.
 11. Theignition apparatus of any one of the preceding claims, wherein thepositioning system further comprises a spool from which the coiledtubing is unspooled.
 12. The ignition apparatus of claim 9, wherein theignition means comprises an oxidant source and oxidant is fed to theignition tool externally of the single tube.
 13. The ignition apparatusof claim 11 or claim 12, wherein the ignition means comprises anignition fuel source and/or ignition chemical source, and ignition fueland/or ignition chemical is fed to the ignition tool via the singletube.
 14. The ignition apparatus of claim 10, wherein the ignition meanscomprises an oxidant source and oxidant is fed to the ignition tool viathe outer tube.
 15. The ignition apparatus of claim 10 or claim 11,wherein the ignition means comprises an ignition fuel source and/orignition chemical source, and ignition fuel and/or ignition chemical isfed to the ignition tool via the inner tube.
 16. The ignition apparatusof any one of the preceding claims, wherein the coiled tubing comprisesheat-exchange formations.
 17. The ignition apparatus of any one of thepreceding claims, wherein the coiled tubing comprises positioners thathelp position the ignition tool within the well channel.
 18. Theignition apparatus of any one of the preceding claims, wherein theignition tool comprises at least one inlet that is in fluidcommunication with at least one tube of the coiled tubing.
 19. Theignition apparatus of claim 18, wherein the ignition tool comprises atleast one outlet that is in fluid communication with the at least oneinlet.
 20. The ignition apparatus of claim 19, wherein the ignition toolcomprises a detachable cap or plug covering the outlet.
 21. The ignitionapparatus of any one of the preceding claims, wherein the ignition toolcomprises a mixing chamber within which ignition fuel, oxidant and/orignition chemical can mix.
 22. The ignition apparatus of claim 21,wherein the mixing chamber contains a Venturi device and/or at least onebaffle.
 23. The ignition apparatus of claim 19 or claim 20, wherein theignition tool comprises a gas diffuser adjacent the at least one outlet.24. The ignition apparatus of any one of the preceding claims, whereinthe ignition tool comprises flow deflectors.
 25. The ignition apparatusof any one of the preceding claims, wherein the ignition tool comprisesheat-exchange formations.
 26. The ignition apparatus of any one of thepreceding claims, wherein the coiled tubing comprises heat-exchangeformations.
 27. The ignition apparatus of any one of the precedingclaims further comprising one or more sensors for sensing and reportingconditions in the ignition tool, adjacent the ignition tool, wellchannel and/or adjacent coal seam.
 28. The ignition apparatus of any oneof the preceding claims further comprising a thermocouple for sensingthe temperature in the well channel, coal seam or ignition tool.
 29. Theignition apparatus of any one of the preceding claims further comprisinga controller operable to trigger ignition, including the provision ofelectrical energy or ignition fuel, oxidant or the release of acombustible ignition chemical.
 30. The ignition apparatus of claim 29,wherein the controller comprises a pipe manifold in fluid communicationwith the coiled tubing and ignition chemical, ignition fuel and/oroxidant sources.
 31. The ignition apparatus of claim 29 or 30, whereinthe controller is operable remotely from the ignition tool to (1)control the ignition fuel/ignition chemical and oxidant ratio of themixture, (2) monitor combustion of the mixture, and (3) control thesupply of electrical energy to the ignition.
 32. A method of igniting anunderground coal seam from within a well channel that extends throughthe seam, said method comprising the steps of (1) moving an ignitiontool of an ignition apparatus into the well channel; and (2) ignitingthe underground coal seam at one or more locations within the wellchannel using the ignition tool, wherein the ignition apparatuscomprises: an ignition system comprising ignition means and the ignitiontool; and a positioning system comprising coiled tubing connected to theignition tool and extendible within the well channel to position theignition tool at a said location within the well channel.
 33. The methodof claim 32, wherein the ignition apparatus is as defined in any one ofclaims 1 to
 31. 34. The method of claim 32 or claim 33 furthercomprising a step of maintaining oxidant in the well channel at a levelto support the combustion.
 35. The method of any one of claims 32 to 34further comprising a step of repositioning the ignition tool to a newignition site in the well channel.
 36. An ignition system comprisingignition means and an ignition tool for igniting an underground coalseam.
 37. The ignition system of claim 36, having features as describedin any one of claims 1 to
 31. 38. Ignition means for igniting anunderground coal seam.
 39. The ignition means of claim 38, havingfeatures as described in any one of claims 1 to
 31. 40. An ignition toolfor igniting an underground coal seam.
 41. The ignition tool of claim40, having features as described in any one of claims 1 to
 31. 42. Apositioning system comprising coiled tubing extendible within a wellchannel to position an ignition tool at a desired location within thewell channel.
 43. The positioning system of claim 42, having features asdescribed in any one of claims 1 to
 31. 44. An ignition system asdefined in claim 36, ignition means as defined in claim 38, an ignitiontool for igniting an underground coal seam as defined in claim 40, or apositioning system as defined in claim 42, and substantially ashereinbefore described in the written description including as shown inthe figures.